The Australian Transport Safety Bureau did not conduct an
on-scene investigation of this occurrence. The report presented
below was derived from information supplied to the Bureau.
While en route from the Jundee mine site to Perth, cruising at
FL220, the crew of the Fairchild Industries Inc Metro 23,
registration VH-WBA, saw the cabin altitude gauge indication
climbing at a rate of about 8,000 ft/minute. The crew, suspecting a
pressurisation failure, donned oxygen masks and directed the
passengers to do the same. They contacted Melbourne Centre air
traffic control and received a clearance to immediately descend to
14,000 ft. Once level at the amended cruise altitude, the use of
passenger oxygen masks was discontinued and the flight proceeded to
Perth.
Company maintenance investigation could not detect the reason
for the pressurisation fault. Extensive trouble shooting was
carried out in accordance with the manufacturer's maintenance
manual, followed by ground runs and a test flight. The aircraft and
its systems performed normally.
The aircraft was placed on a maintenance watch and returned to
service where it has since operated without incident.